This invention relates to lift door control apparatus.
It is the practice to control the operation of electrically-operated lift car doors to ensure that they do not open when the car is between floors, either during normal operation or in the event of a power failure. This is normally achieved by an arrangement including a release arm mounted on the car which engages with ramps located one at each floor. Unless the release arm is engaged and deflected by a ramp, the door operating mechanism is locked and disabled.
In the event of a power failure, if the car is winched to a floor the release arm will be deflected by the floor ramp and unlock the door operating mechanism. However, there will be no power to energise the operating mechanism. It is common practice to design such door operating mechanism so that there is a strong mechanical resistance to any attempt to initiate opening of the door manually. This is achieved by arranging for the radius arm of the operating mechanism to be at or near a top-dead-center position in relation to its associated drive wheel, such arrangements being well-known and not requiring further description. The resulting situation is that assistance must be called to apply a strong force to the door, as by employing a crow-bar, with the consequent delay in releasing the car passengers and inevitable damage to the car door and operating mechanism.
Furthermore, it is also common practice to provide that while the car is travelling through intermediate floors to its selected destination floor during normal operation, the release arm is held by an electro-magnetic actuator in a retracted position in which it will not engage the ramps of intermediate floors.